1. Technical Field
The present invention relates to a liquid ejecting head and a liquid ejecting apparatus, each including a pressure generating chamber communicating with a nozzle aperture and a piezoelectric element that includes a piezoelectric layer and electrodes applying a voltage to the piezoelectric layer and functions to change the pressure in the pressure generating chamber, and relates to the piezoelectric element.
2. Related Art
Some piezoelectric actuators used in liquid ejecting heads include a piezoelectric element having a structure in which a piezoelectric layer made of a piezoelectric material capable of electromechanical conversion, such as a crystallized dielectric material, is disposed between two electrodes. Ink jet recording heads are a typical type of liquid ejecting head. An ink jet recording head includes a vibration plate defining a part of a pressure generating chamber communicating with nozzle apertures through which ink droplets are ejected. In the ink jet recording head, a piezoelectric element deforms the vibration plate to apply a pressure to the ink in the pressure generating chamber, thereby ejecting ink droplets through the nozzle apertures.
The piezoelectric material (piezoelectric ceramic) used for forming the piezoelectric layer of such a piezoelectric element is required to have high piezoelectric properties, and a typical example of the piezoelectric material is lead zirconate titanate (PZT) (JP-A-2001-223404).
On the other hand, it is desirable to reduce lead from piezoelectric materials, from the viewpoint of environmental protection. An exemplary lead-free piezoelectric material is BiFeO3, which has a perovskite structure expressed by ABO3. In the ABO3 structure, A represents the A site and has 12 oxygen ligands, and B represents the B site and has 6 oxygen ligands. However, for example, BiFeO3-based piezoelectric materials are less insulating and liable to cause leakage current. If leakage current is liable to occur, the material is likely to crack when it is used while a high voltage is applied, and is therefore difficult to use in a liquid ejecting head. Accordingly, piezoelectric materials used in piezoelectric elements are required to have a high insulation value of 1×10−3 A/cm2 or less in use, for example, at a typical driving voltage of 25 V.
This issue arises not only in ink jet recording heads, but also in other liquid ejecting heads that eject droplets other than ink, and piezoelectric elements used for applications other than liquid ejecting heads have the same issue. Furthermore, leakage current results in a serious problem that the energy consumption of the piezoelectric element is increased when the piezoelectric element is used as a sensor. It is desirable that leakage current be low as well in piezoelectric elements used for piezoelectric sensors, infrared sensors, thermal sensors and pyroelectric sensors that are used at an applied voltage of, for example, 1 V or less.